textproduct: Quad Cities

KEY MESSAGES

- The wet weather pattern will continue through the weekend with rounds of rain which may be heavy at times. There will be periods of dry weather between each round.

- The repeated rounds of rain will result in general rises on the Mississippi River with the potential for river flooding on tributary rivers.

SHORT TERM /THROUGH FRIDAY/

Issued at 200 PM CDT Thu Sep 17 2026

As of early this afternoon, a quasi-stationary front was draped across eastern Iowa into northwest Illinois, approximately along the I-80 to Highway 30 corridor. GOES visible imagery showed widespread low clouds north of the front where temperatures were in the upper 60s to mid 70s. Mainly clear skies were noted south of the boundary and temperatures were much warmer into the 80s (~upper 80s south of Highway 34), accompanied by very humid conditions with dewpoints in the lower to mid 70s. This hot and humid air mass has pushed heat indices into the mid 90s to near 100 degrees across the far south.

Heading into tonight, winds will shift to the east-northeast in response to surface cyclogenesis along the Front Range in Colorado. A wave of warm air advection aloft may lead to scattered showers and isolated storms (20-60%) late tonight into Friday morning, working west to east through portions of the area. Highest chances for some measurable rain are to the west and northwest of the Quad Cities. This activity looks to move through relatively quickly, thereby limiting total rainfall amounts with much of the area receiving under 0.25". A few isolated showers and storms remain possible through Friday afternoon, but with most of the area likely to stay dry during this period.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Issued at 200 PM CDT Thu Sep 17 2026

The lobe of mid-level vorticity that spawned the Colorado low moves into the Upper Mississippi River Valley before being ejected eastward by the zonal flow. This drags the low pressure center northeastward towards Iowa. As the winds shift to out of the southeast, a warm, moist air is pulled northward into the CWA, setting the stage for another round of heavy rain north of I-80 Friday night into Saturday morning. Latest ensemble guidance shows a swath of 0.25-0.75 of an inch along the Highway 20 corridor (50-70% chance). The coverage and intensity of these storms will decrease throughout the day on Saturday but remain scattered north of I-80 as the low pressure center drifts into northern Iowa.

Saturday night-Monday...A shortwave trough that has been camping across the western CONUS for most of the week will finally propagate eastward into the Northern Rockies Saturday night. Shortwave ridging over the Mid-to-Upper Mississippi River Valley introduces southwesterly flow aloft, pulling another mid-level vorticity lobe northward into the north-central Plains. This mid-level trough is forecasted to redevelop storms (50-70% coverage) along a cold front moving through the area. The SPC has a Marginal Risk, Level 1 out of 5, for most of the outlook area for isolated damaging winds, but the latest LREF guidance only has a 20-40% joint probability of SBCAPE exceeding 500 J/kg and the sfc-to-500 mb bulk shear exceeding 30 knots. Therefore, any convection that forms should struggle to organize.

After Saturday night, scattered PoPs (40-70%) will stick around into Monday as weak shortwaves rotating around the main trough axis, now over the Northern Plains, keeps CVA over the area. By Monday though, most precipitation will be in the form of rain showers as the boundary and low pressure over Missouri drifts further south and northeasterly flow from a high pressure over Ontario pumps in cooler air.

Tuesday-Wednesday...The shortwave trough over the Northern Plains finally reaches the Midwest on Tuesday. Isolated cold- core showers could stick around during the day before subsidence sets in on the backside of the trough heading into Tuesday night and Wednesday. The persistent northeasterly flow should allow for seasonably cool temperatures with highs only in the lower to upper 60s!

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1250 PM CDT Thu Sep 17 2026

A warm and humid air mass will remain over the area into Friday, and with light winds resulting in little boundary layer mixing, periods of MVFR/IFR ceilings are likely. Scattered showers and isolated storms are possible Friday AM with low confidence on coverage this far out (20-40%). Patchy fog may develop tonight which could lead to periods of MVFR/IFR visibilities; however, confidence is very low on the extent and severity.

DVN WATCHES/WARNINGS/ADVISORIES

IA...None. IL...None. MO...None.